1. Field of the Invention
This invention relates generally to fluid valves, and is concerned in particular with a regulating valve that operates in response to a variable fluid inlet pressure above a selected threshold level to deliver the fluid at a constant outlet pressure and flow rate. A closure mechanism is selectively operable either to accommodate the valve's normal pressure responsive regulating functions, or to override such functions by maintaining the valve in a closed state at inlet pressures both above and below the threshold level.
2. Description of the Prior Art
Examples of known regulating valves are described in U.S. Pat. Nos. 6,026,850 and 6,209,578. Such valves are normally closed in response to fluid inlet pressures below a threshold level, and operate in a modulating mode in response to variable fluid inlet pressures above the threshold level to deliver fluids at constant outlet pressures and flow rates. However, at fluid inlet pressures above the threshold level, such valves remain open and cannot serve as shut off valves, thus making it necessary to employ additional and separately operable valves to achieve this added function.